1. Field of the Invention
The present invention relates generally to methods and devices for analyzing and mapping soil properties within a field. In particular, the present invention relates to methods and devices for mapping soils within a field in three dimensions using multiple sensors.
2. Description of the Related Art
Mapping soil properties precisely, especially identifying differences hidden within the soil profile, has proven challenging for soil scientists and soil classifiers. While GPS technology provides precise positional information, quantitative information about the soil properties that exist within the profile at each location remains a limiting factor. The number of soil samples needed to accurately map soil variability is impractical using conventional sampling and analysis methods.
One of the important issues involving in situ soil measurements relates to reducing atmospheric carbon by increasing the amount of carbon stored in the soil. For carbon-trading to include agricultural soil sequestration, accurate baseline estimates of soil carbon, coupled with equally precise follow-up measurements, must be achievable. Two aspects of soil carbon makes this especially challenging: 1) expected carbon increases are small relative to the amount of carbon variability within the field, and 2) changes in soil bulk density must also be measured. Both of these measurements are traditionally accomplished in a laboratory, which requires extracting soil from the field, transporting to the lab, drying, and measurement. The cost for each sample result precludes intense sampling and analysis.
Rapid investigation using soil sensors can address this problem, provided the sensing technology relates to the soil properties of interest. Soil measurements using diffuse near-infrared spectroscopy (NIR) have been shown to relate closely to soil carbon levels. Reflectance in the visible (VIS) and in the NIR portion of the electromagnetic spectrum are highly influenced by molecules containing strong bonds between relatively light atoms. These bonds tend to absorb energy at overtones and combinations of the mid infrared fundamental vibration frequencies. The predominant absorbers in this region are the C—H, N—H, and O—H functional groups, making the VIS-NIR region ideal for quantifying forms of carbon, nitrogen and water respectively. Soil electrical conductivity (EC) has been shown to relate to soil texture and soil moisture. Soil penetrometer probes measuring insertion force have been shown to relate to soil compactness. Since the factors affecting bulk density are soil moisture, texture, and compaction, using sensors to measure these factors individually holds significant potential for developing calibrations to soil bulk density.
Soil heterogeneity within a field and within the profile prevents simple characterization of soils. A device that maps the field in the X-Y direction, but at only one depth, would not identify changes in the profile. A device that probes into the profile, but at a limited and random number of sites, would likely not be able to capture all the variability within the field.
There is a need in the industry for a system that characterizes the X-Y variability of soils in a field, identifies areas that require profile investigations, and characterizes the −Z variability at those sites.